The invention relates to a process for the production of yeast autolysate, the yeast autolysates produced by the process, as well as their use in foodstuffs and feed.
Extracts from yeasts were originally used as substitutes for meat extracts for the aromatization of foods and animal feeds for pets and domesticated animals. The importance of yeast extracts as a natural aroma substance has increased in the course of the last decades. Technically extracts from yeasts can be produced in various ways. The processes differ both in their basic procedure and in the functional properties of the products obtained. The three variants for yeast extraction are plasmolysis, autolysis and hydrolysis. Production of yeast extracts by autolysis has the greatest technical importance. The production of yeast extracts by autolysis, called yeast autolysates in the following, is described in the textbook "Die Hefen" (The Yeasts), Vol. II, pp. 761-764 (published by H. Carl Nurnberg, 1962), as well as in the journal "Process Biochemistry", Vol. 1, pp. 313-317 (1966) and Vol. 5, pp. 50-52 (1970).
Suitable for the production of yeast autolysates are several genera of yeast, which are grown on different carbon sources. On an industrial scale, fast-growing yeasts of the genera Saccharomyces, Candida and Torula are cultivated on cheap carbon sources, such as molasses, malt extract, whey, sulfite liquor, ethanol and/or alkanes.
The nutrient value of living yeasts is low. Due to the separation of the yeast cell walls and due to the hydrolytic degradation of the cell content substances, the yeast autolysates have higher nutrient values and better aroma properties. The important thing in making yeast extract by means of autolysis is to start the hydrolytic degradation of the cell content substances by cell-specific enzymes without destroying the hydrolytically active enzymes by means of the necessary impulse which stimulates the living yeast to self-digestion. The hydrolytic degradation of the cell content substances can be released by destruction of the yeast cell structures by grinding or bursting. However, these processes also often release the necessary impulse to self-digestion. Suitable equipment for these process steps are known, but they require an additional high expenditure of energy. By drying the yeast before the autolysis, the cell membranes become labile and the autolysis of the resuspended yeast is supported (DOS No. 23 59 501). Most frequently, organic solvents are used for the labilization of the cell membranes and support of the autolysis ("Die Hefen", Vol II, pp. 761-764). The use of solvents such as ethanol, ethyl acetate, toluene and chlorinated hydrocarbons is preferred. In more recent processes the lysis of the yeast cells is initiated by added enzymes from various micro-organisms.